1. Field of the Invention
The present invention relates to a method and an apparatus for treatment of an effluent containing radioactive materials, and especially relates to a method and an apparatus suitable for treatment of an effluent containing radioactive materials which is drained from a nuclear power plant.
Priority is claimed on Japanese Patent Application No. 2006-245293, filed Sep. 11, 2006, the content of which is incorporated herein by reference.
2. Description of Related Art
Regarding a method and an apparatus for treating an effluent containing radioactive materials, an effluent treatment apparatus using a microfiltration filter, particularly a hollow fiber membrane type microfiltration filter, has been applied in recent years in a treatment system for an effluent containing radioactive materials (radioactive waste water) such as an effluent containing radioactive materials drained from a nuclear power plant. Such an apparatus used for treating an effluent containing radioactive materials generally includes a demineralizer such as a mixed-bed type ion-exchange resin tower which is provided at the downstream position of a filter. For example, a treatment system as shown in FIG. 4 has been used wherein an effluent containing radioactive materials is kept at first in a storage tank 101 for an effluent containing radioactive materials, and then the effluent is sent from the tank to a hollow fiber membrane filtration tower 102 to filter the effluent, and subsequently, the obtained filtrated water is passed through a mixed-bed type ion-exchange resin tower 103 to conduct demineralization. Said treatment system is structured in general such that plural systems are provided separately, from the viewpoint of conducting treatments with high efficiency according to each property (water quality) of each discharged effluent containing radioactive materials. (For example, Japanese Unexamined Utility Model Application, Second Publication No. 6-34720.) However, there is a disadvantage in a space when plural apparatuses or the like used for said separate plural treatment systems are required to be placed according to plural kinds of discharged effluent containing radioactive materials. Accordingly, a method has been proposed in recent years wherein ion-loaded waste liquids such as an equipment drain effluent generated from each peace of equipments and floor drain effluent generated from each building, which can be treated comparatively easily, are treated together using the same system and apparatus.
Differential pressure of a filtration apparatus (microfiltration filter) increases gradually due to an organic substance, bacteria, submaterials used at the time of plant inspection or the like, which are included in an effluent, when a radioactive waste liquid (an effluent containing radioactive materials) is treated in such a system wherein a microfiltration filter is provided and a demineralization tower is arranged in a downstream position of the microfiltration filter as described above. Particularly, a floor drain effluent containing radioactive materials includes comparatively large amounts of impurities such as an organic substance and bacteria, and the differential pressure of the filtration apparatus tends to increase earlier when said floor drain effluent is treated. Filtration efficiency or the like deteriorates when the differential pressure of the filtration apparatus increases. Therefore, in order to return the increased differential pressure to a normal level of differential pressure, a periodic recovery treatment is conducted wherein the operation of an apparatus used for treating an effluent containing radioactive materials is stopped and then chemical cleaning for the filtration apparatus is conducted using an oxidizing agent such as hydrogen peroxide regularly. When the differential pressure of the filtration apparatus, specifically a difference between pressures prior to and after passing through the filtration apparatus, increases, the differential pressure can be reduced by conducting chemical cleaning using an oxidizing agent. However, there are further demands for decreasing the number of chemical cleaning operations to as few as possible, in order to decrease the burden of an operator, to prevent oxidation deterioration of a filtration film and the like.
Moreover, regarding the control of an increase of differential pressure of a filtration apparatus, it has been described in (although the following documents do not disclose a system for treatment of an effluent containing radioactive materials) Japanese Unexamined Patent Application, First Publication, Nos. Sho 63-80896 and Hei 9-38648, that an increase of differential pressure of a filtration film can be suppressed due to the addition of a trace amount of an oxidizing agent which is injected continuously or intermittently at an upstream position of a filtration apparatus. However, although an effect for suppressing an increase of the differential pressure of the filtration film may be observed, oxidization deterioration of an ion-exchange resin provided at a downstream position of the filtration apparatus may occur if such a method wherein an oxidizing agent is injected is used. Accordingly, such a method has not been adopted in any system for treating an effluent containing radioactive materials, particularly in a system for treating an effluent containing radioactive materials which is generated in a nuclear power plant.